Problem: In math class, the girl to boy ratio is $6$ to $8$. If there are a total of $42$ students, how many girls are there?
Answer: A ratio of $6$ girls to $8$ boys means that a set of $14$ students will have $6$ girls and $8$ boys. A class of $42$ students has $3$ sets of $14$ students. Because we know that there are $6$ girls in each set of $14$ students, the class must have $3$ groups of $6$ girls each. There is a total of $18$ girls in math class.